1. Field of the Invention
The present invention relates to a drilling and/or percussive hammer having no-load operation control according to the preamble of patent claim 1.
2. Description of the Related Art
Such a drilling and/or percussive hammer (hereinafter simply called “hammer”) having an application pressure-dependent no-load operation control is known from DE 101 45 464 A1. There, the hammer has a no-load channel for connecting a hollow space, formed between a drive piston and a percussion piston in a pneumatic spring percussion mechanism, to the surrounding environment, said channel being capable of being opened and closed by a valve. In the flow of force between the grip point of the handle and the hammer housing, there is situated an acquisition device for acquiring an application force that can be applied to the handle by the operator. The valve can be controlled dependent on the acquired application force.
The resulting advantages are described in detail in DE 101 45 464 A1. In particular, in this way it is possible for the operator to place the hammer at first gently onto the stone that is to be worked, even if the motor is already activated, and therefore has an increased rotational speed. In this state, the percussion mechanism is still in no-load operation, even if the drive piston in the percussion mechanism is already moved back and forth. The valve is not actuated, with closing of the no-load channel, until the application force is increased by the operator, whereupon an air spring can form in the hollow space between the drive piston and the percussion piston. In this way, percussion operation begins.
The hammer described in DE 101 45 464 A1 has proved its usefulness in practice. However, it has turned out that the design described there can be further improved. In particular, due to the fact that during the transition from no-load operation to percussion operation the hammer carries out certain intrinsic movements due to the actuation of the pneumatic spring percussion mechanism and the oscillations that arise therefrom, so that the hammer housing moves relative to the handle held by the operator, it is possible for the valve to close prematurely, so that in the end percussion operation begins suddenly, in a manner that is not anticipated by the operator.